The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
A typical vehicle engine relies on internal combustion within engine cylinders to provide torque. A spark generated by a sparkplug ignites a mixture of air and fuel within the cylinders to cause combustion. Spark timing and control of the air/fuel mixture determine the performance of the engine.
Internal combustion engine control systems are typically steady-state, throttle-based control systems. In the steady-state control systems, the torque output of the engine is adjusted to match a load placed on the engine. The load on the engine can change. For example, the load can be changed by a driver adjusting a position of an accelerator pedal. The engine control system adjusts the operation of the engine to match the changing load placed on the engine.
The engine control system selects a spark timing for the engine primarily as a function of the engine speed (RPM) and load. Compensation can be made for other factors (e.g., temperature, altitude, and other environmental conditions). The spark timing is selected from a set of tables accessed by the engine control system.
The values of spark timing in the tables are typically set to achieve mean best torque for the associated operating conditions. Operating at the mean best torque results in the best brake-specific fuel consumption at stoichiometry. The spark timing in these tables is generated on an engine dynamometer on a few engines and then adjusted on the vehicle during development. These values of spark timing are programmed into the memory accessed by the engine control system and used on all engines for that application. The values of the spark timing that generate the best torque are usually borderline with detonation. To avoid premature detonation, a knock sensor in conjunction with a knock detection algorithm can retard the spark advance from the timing value provided by the table.
Due to production differences during manufacturing and aging of the engine and associated components through its lifespan, the spark timing for mean best torque can differ from the programmed tabulated data utilized by the engine control system. Thus, the spark timing in the tabulated data can result in not achieving the mean best torque and, as a result, not achieving the best brake-specific fuel consumption at stoichiometry.